1. Field of the Invention
The present invention relates to a process for producing a highly pure phenol, which comprises of removing impurities contained in a crude phenol obtained from an acid-decomposition product of cumene hydroperoxide. More specifically, it relates to a process for producing a highly pure phenol, which comprises of converting impurities contained in the above crude phenol into high-boiling compounds without causing a substantial loss of useful substances contained in the crude phenol, and recovering a phenol by distillation.
2. Related Art
As an industrial process, there is known a process for producing a phenol in which cumene hydroperoxide obtained by oxidation of cumene is acid-decomposed. The acid-decomposition product obtained by this process contains cumene, phenol, .alpha.-methylstyrene and acetone as main components along with a small amount of by-products. Meanwhile, a phenol is used as a raw material for producing diphenylolpropane, polycarbonate, etc., and the phenol as a raw material for these is required to have a high purity.
As far as the phenol for the above use is concerned, the content of hydroxyacetone (HA) as one of the impurities is required to be 30 ppm or less, preferably 10 ppm or less, and the total amount of aliphatic and aromatic carbonyl compounds (total carbonyl amount) other than HA is required to be 100 ppm or less, preferably 50 ppm or less.
For obtaining a highly pure phenol satisfying the above-described quality, it is general practice to carry out the following treatment for removing impurities. That is, a crude phenol, which is obtained by removing a large part of the low-boiling substances such as acetone, cumene, water and .alpha.-methylstyrene and a large part of the high-boiling substances such as acetophenone and .alpha.-dimethylphenylcarbinol from a neutralized acid-decomposition product by fractional distillation, is further purified to remove aliphatic carbonyl compounds such as hydroxyacetone (HA) and aromatic carbonyl compound such as .alpha.-phenylpropionaldehyde.
In conventional methods for producing a highly pure phenol, for example, Japanese Patent Publication No. 11,664/1962 discloses a method in which a crude phenol (containing 200 ppm of hydroxyacetone) is catalytically treated with an active alumina catalyst at 360.degree. C. to allow the hydroxyacetone to react with a phenol to convert it into 2-methylbenzofuran (2-MBF), and phenol. The 2-methylbenzofuran are separated from each other by steam distillation. Further, Japanese Patent Publication No. 1,289/1979 discloses a method using an active alumina for purifying crude cresols.
Further, Japanese Patent Publication No. 12,250/1967 discloses a method in which a crude phenol is catalytically treated with a silica-alumina catalyst at 150.degree. to 250.degree. C. to convert carbonyl compounds into other compounds, and they are separated from a phenol by steam distillation. Furthermore, British Patent 1,231,991 discloses a method in which a crude phenol containing no water is catalytically treated with an acidic ion-exchange resin catalyst at 80.degree. to 150.degree. C. to convert carbonyl compounds to other compounds, and they are separated from a phenol by steam distillation.
The above methods are all directed to a method in which impurities are converted to other compounds. The defect with these methods is that phenol and .alpha.-methyl styrene as useful components react with impurities or respectively undergo condensation to form cumylphenol or dimer of olefin and thus, the useful components are wasted.